In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of minaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers (248 nm) have become the center of mass production, and ArF excimer lasers (193 nm) are now also starting to be introduced in mass production. Further, research is also being conducted into lithography techniques that use F2 excimer lasers (157 nm), extreme ultraviolet radiation (EUV), electron beam (EB) and the like as the light source (radiation source).
Resists for use with these types of short wavelength light sources require a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of short wavelength light sources.
One example of a known resist that satisfies these conditions is a chemically amplified resist, which includes a base resin and an acid generator that generates acid upon exposure.
These chemically amplified resists include positive resists in which the alkali solubility of the exposed portions increases, and negative resists in which the alkali solubility of the exposed portions decreases.
Until recently, polyhydroxystyrene (PHS) or derivative resins thereof in which the hydroxyl groups are protected with acid-dissociable, dissolution-inhibiting groups (PHS-based resins), which exhibit high transparency to KrF excimer lasers (248 nm), have been used as the base resin component of chemically amplified resists. However, because PHS-based resins contain aromatic rings such as benzene rings, their transparency is inadequate for light with wavelengths shorter than 248 nm, such as light of 193 nm. Accordingly, chemically amplified resists that use a PHS-based resin as the base resin component suffer from low levels of resolution in processes that use light of 193 μnm.
As a result, resins that contain structural units derived from (meth)acrylate esters within the principal chain (acrylic resins) are now widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1).
Further, such resists are required to exhibit not only excellent properties with respect to sensitivity and resolution, but also various lithography properties such as depth of focus (DOF) and shape of the resist pattern.
In addition to these properties, due to the recent requirement for resist pattern with high resolution, improvement in defects (surface defects) in resist pattern following developing is also required.
Defects refers to general abnormalities of a resist pattern, which are detected when observed from right above the developed resist pattern, using a surface defect detection equipment (trade name: “KLA”) manufactured by KLA-TENCOR CORPORATION.
Examples of these abnormalities include post-developing scum, foam, dust, bridges across different portions of the resist pattern, color irregularities, and foreign deposits. Especially, in lithography technique using ArF excimer lasers and lithography techniques developed thereafter such as lithography technique using F2 excimer lasers, EUV, electron beam (EB) and the like as the light source, when a fine pattern such as a resist pattern of no more than 130 nm is formed, these defects are becoming of serious problems.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-167347